Though I create a complex world in which my characters live, my readers only encounter a fraction of what I know of it. Only the tip of the iceberg is experienced by the readers, and that’s good! The action would be smothered in exposition if the whole iceberg were hauled out onto the page.
I learned this the hard way, burying the action in my stories with details of setting. The general rule I eventually came up with is this: Reveal only as much information as is absolutely necessary for the reader to understand the action at hand.
The best example of this sort of narrative economy I’ve ever read is in Michael Swanwick’s Stations of the Tide, for which he deservedly won the 1991 Nebula for best novel. In fact, the economy is so severe in that novel that at times I felt my head spinning. (What the hell’s a surrogate? He doesn’t explain it. He just names it and moves on!) And I enjoy that as a reader: he doesn’t hold my hand, he makes me work.
All the same, that kind of economy is probably why it won the Nebula, which is voted in by fantasy/scifi authors, rather than a Hugo, which is voted in by fans.